Thermal transfer printing receiver

Abstract

A thermal transfer printing receiver sheet for use in security laminates, comprises a substrate supporting a receiver coat of a dye-receptive composition on one side and a backcoat on the other, wherein the backcoat comprises a thermoplastic polymer having a Tg less than 130 DEG C., and dispersed therein a particulate solid material in amount 1-24% by weight of the thermoplastic polymer and an average particle size of 0.3-10 mu m. The security laminates are prpared after printing the receiver with an image, by bonding a first cover sheet of plastics material to the printed receiver coat so as to overlie the image, and a second cover sheet of plastics material can be bonded to the present backcoat more readily than to a highly crosslinked backcoat, using common adhesives. For greater security, thicker than normal backcoats are used.

We claim: 
     
       1. A thermal transfer printing receiver sheet comprising a substrate supporting a receiver coat of a dye-receptive composition on one side and a backcoat on the other, characterised in that the backcoat comprises a thermoplastic polymer having a Tg less than 130° C., and dispersed therein a particulate solid material in amount 1-24% by weight of the thermoplastic polymer and an average particle size of 0.3-10 μm. 
     
     
       2. A thermal transfer printing receiver sheet as claimed in claim 1, characterised in that at least a major proportion of the thermoplastic polymer of the backcoat is an amorphous polyester. 
     
     
       3. A thermal transfer printing receiver sheet as claimed in claim 2, characterised in that the polyester has a Tg of between 20° C. and 85° C. 
     
     
       4. A thermal transfer printing receiver sheet as claimed in claim 2, characterised in that the thermoplastic polymer comprises a mixture of a polyester and a styrene-maleic anhydride copolymer. 
     
     
       5. A thermal transfer printing receiver sheet as claimed in claim 2, characterised in that the polymer comprises a mixture of a polyester and a butylated melamine formaldehyde resin. 
     
     
       6. A thermal transfer printing receiver sheet as claimed in claim I, characterised in that the particulate material comprises particles having an average size of 0.3-2 μm in an amount of 1-15% by weight of the thermoplastic polymer. 
     
     
       7. A thermal transfer printing receiver sheet as claimed in claim 6, characterised in that the particulate material consists essentially of a micronised solid in amount of about 1.5% by weight of the thermoplastic polymer. 
     
     
       8. A thermal transfer printing receiver sheet as claimed in claim 1, characterised in that the backcoat has a thickness of at least 4 μm. 
     
     
       9. A thermal transfer printing receiver sheet as claimed in any one of claims 1 to 8, characterised in that a) the receiver coat contains at least one thermal transfer dye located in selected positions to form an image,   b) a first cover sheet of plastics material is bonded to the printed receiver coat to overlie the image, and   c) a second cover sheet of plastics material is bonded to the backcoat.   
     
     
       10. A security laminate comprising an information sheet printed with an information-containing image and having a protective cover sheet bonded to each side, characterised in that the information sheet is a thermal transfer printing receiver sheet comprising a substrate supporting on one side a receiver coat of a dye-receptive composition containing at least one thermal transfer dye located in selected positions to form the image, and on the other side a backcoat comprising a thermoplastic organic polymer having a Tg less than 130° C., and dispersed therein a particulate solid material in amount 1-24% by weight of the thermoplastic polymer and an average particle size of 0.3-10 μm; a first of the cover sheets being formed of a plastics material which is bonded to the printed receiver coat to overlie the image, and a second of the cover sheets being formed of a plastics material which is bonded to the backcoat.